The invention relates to a plasma cutting torch comprising a torch nozzle whose two electrode holders are adapted to be connected with different poles of a power supply and are coaxially arranged to form a flow path for gas for operation of the torch, an insulating ring, preferably made of ceramic material, being present between the holders to relatively locate the holders in axial and radial directions.
A plasma cutting torch, having these features, has been proposed in the German unexamined specification Nos. 3,400,281 and 3,400,282. In these earlier designs the two electrode holders were fashioned with steps bearing on the insulating ring at points which were diagonal in relation to the cross section of the ring in such a way that each electrode holder only had one axial bearing surface placed obliquely opposite to the axial support surface of the other electrode holder. Experience since gathered with this set-up has however shown that when it has been heated up relative radial displacement of the two electrode holders, and therefore of the two electrodes (constituting the torch nozzle and the nozzle needle), may take place, owing to the differential thermal expansion of the insulating ring and the electrode holders. The consequence of such relative motion is that the coaxial status of the two electrodes, and thus the precisely centered location of the electrode needle, will be lost. This in turn will lead to increased wear of the electrodes, more especially of the torch nozzle for the one electrode.